Inside the Collapse of Earth's Largest Penguin Colony

In the storm-driven wilderness between South America’s southern cape and the frozen boundary of mainland Antarctica, the South Sandwich Islands form an isolated, crescent-shaped archipelago of rock and ice. Its rugged, northernmost isle, Zavodovski Island—where chinstraps and macaroni penguins blanket the hillsides that surround an active volcano—has held the title of the largest penguin colony on Earth.

But as chinstrap penguins began facing steep decline across the Antarctic Peninsula starting in the 1980, scientists wondered whether this remote island was faring any better.

Through an analysis combining aerial drone surveys and manual population counts, researchers from the British Antarctic Survey (BAS) have discovered that in fewer than fifteen years, the island’s chinstrap population has plummeted by 63 percent—a loss of over half a million penguins.

Their findings, published today in the journal Current Biology, identifies the island as home to the fastest-declining chinstrap population in the world, with climate-driven losses documented continuously since 2011. The decline wipes out more than a quarter of the total penguin population on Zavodovski, ceding the island's title of world's largest penguin colony to Cape Adare in Antarctica’s Ross Sea.

“A 63 percent loss in 15 years means over half a million nests are gone. Imagine losing 60 percent of a country’s entire population in that timeframe. It’s really concerning,” says Lucas Krüger García, a polar scientist and seabird ecologist for a Chilean research center who was not involved in the study. “The fact that this single colony represented 30 percent of the global chinstrap population makes it even more concerning.”

The Southern Ocean is no stranger to loss. This news comes just six months after Emperor penguins and Antarctic fur seals were officially declared endangered with declining sea ice levels cited as a leading culprit. Acting as the planet’s primary climate buffer, the Southern Ocean absorbs nearly three-quarters of global ocean warming and a fifth of man-made carbon.

Below the surface, warm intermediate waters are melting the continental shelf, while deeper ocean layers in Antarctica’s Weddell Sea are warming up to five times faster than the global ocean average at equivalent depths—dismantling the frozen platforms that sustain Antarctic marine life.

Chinstrap penguins are what scientists describe as specialists—they primarily eat a tiny crustacean called krill. This leaves them uniquely vulnerable to changes in their ecosystem as rising temperatures fundamentally transform their habitat from snow and ice to bare rock. Krill depend on sea ice for food and shelter, and just a single degree of warming disrupts this fragile balance, causing severe krill shortages.

“The Southern Ocean is changing rapidly, more rapidly at the moment than anywhere else on the planet,” says Peter Fretwell, a remote sensing expert for the BAS and co-author of the study. “What we're seeing in Antarctica now is an early warning of what's to come over the rest of the world.”

In December of 2023, Fretwell’s BAS colleagues sailed into some of the most hostile waters on the planet to study this colony. The scientists arrived at Zavodovski after fifteen days of navigating hostile seas.

On shore, they were met with pungent volcanic fumes and penguin guano. The island’s surrounding coastal features have names like Acrid Point, Stench Point, Reek Point, Pungent Point, and Noxious Bluff. While they found far fewer than expected chinstrap penguins on the island, the nearby population of macaroni penguins was growing; their numbers increased by around 28 percent between 2011 and 2016.

“The area is transitioning into a sub-Antarctic state, so we’re losing the more maritime Antarctic chinstraps, and we’re gaining macaroni penguins because the ecosystem is getting more suitable for the warmer water species,” says Norman Radcliffe, a seabird ecologist at BAS and the study’s lead author.

Macaroni penguins nest on rocky surfaces, remain near their colonies year-round, and–crucially –switch their diet to fish when krill become scarce.

The research team pinpointed the culprit for chinstraps’ steep decline by systematically eliminating other potential culprits: The island has ample space for nesting, which means interspecies competition was unlikely. Local krill fishing is banned within the island’s Marine Protected Area, suggesting overfishing wasn’t eliminating penguin prey. And a 2016 volcanic eruption may have killed some of the chinstrap population, but did not alter the data showing a steady, decade-long decline. Instead, the study authors say the chronic drop points squarely to regional ocean warming and sea-ice loss—though questions remain about how off-site krill fishing along connected ocean currents might worsen the strain.

Long term, scientists expect climate change to reduce the region’s overall biodiversity.

“What we’re looking at in the long run is a loss of diversity,” Fretwell says of the continent's wildlife. “We'll get some generalists who are going to do well and move into those habitats, but we will lose species that are specialists and have a small ecological niche... and a limited breeding range.”

Experts say Zavodovski’s chinstrap penguins are unlikely to seek out more habitable waters on mainland Antarctica.

“A lot of people think that animals move south, but generally penguins are quite site-faithful, and they stay where they are,” Fretwell explains.

For many scientists, these shifts on Zavodovski are a bellwether for far broader ecological disruptions worldwide.

“Not long ago, this island was considered a pristine ecosystem, but this species has now strongly felt the impacts of climate change,” notes Krüger García, “This study confirms what we have unfortunately suspected, which is that it really isn’t doing well. It's one species, but it's a symptom of a way larger problem. It’s a canary in a coal mine.”